SPACE SOLAR PLASMA PHYSICS

Eruptive prominence observed by EIT (ESA/NASA) consortium
 
 

FINAL REPORT

OUTLINE OF THE PROJECT
 

The sun and the Heliosphere are our closest astrophysical laboratories. Our life is effected from the activity of our star. The sun is active and undergoing dramatic explosions that effect the life here in earth. Our dependence on the large fleet of satellites traveling near earth makes the study of the explosive events a necessary subject for the next decade. The three events supported by EEC have analyzed in depth the physical processes taking place in the solar interior and the solar atmosphere and how they effect the Heliosphere. The major energy source for our lives here in Earth is in the core of the sun. The transfer of energy from the sun to Earth is a difficult scientific problem due to the large number of different scales involved in the physical processes taken place in the energy propagation from the Sun’s core to the outer Helliosphere.

In all three events organized in different European cities, the solar interior, the solar atmosphere the solar wind were studied. Substantial emphasis was given to the study of the explosive events (flares and Coronal Mass Ejection (CME)).

The first event was organized in Halkidiki, near Thessaloniki, Greece. More than 150 scientists attended and a substantial fraction of them were young graduate students and post doctoral. The major part of the EEC funding was directed to young participants and the invited speakers. The proceedings were published by Springer Verlag (Lectures in Physics series).

The second event was organized in Orsay, near Paris. The subject of the conference was “Space solar physics.” It attracted 60 young participants and around 10 lecturers. The proceedings were published by Springer Verlag (Lectures in Physics series). The funding was directed mostly to the young scientists and the lectures.

The third and final event was held in Florence. It attracted almost 250 participants and a substantial number of young scientists. The meeting was considered a major success and mapped the strategy for our research in Solar physics for the next millennium. The proceedings were published by ESA.

Several invited reports, presented during the meeting, have demonstrated major departures from our traditional view of the structure of the solar atmosphere and its interaction with the Heliosphere. It is worth mentioning a few:

Paterno(Italy) discussed recent results from the helioseismic networks IRIS and BISON which permitted to measure the lowest degree p-mode splitting and infer the rotation of the central region of the Sun below 0.3 Ro. We expect to learn a lot from the detection and identification of g-modes (if they exist) from the forthcoming data from Golf instrument on SOHO satellite.

The solar activity is apparently chaotic and is consistent with the observed behavior of other stars of similar age and mass. The crucial parameter is the rotation rate W , which decreases a star grows older owing to magnetic breaking. Weiss(UK) reported an elegant way to explore the solutions of this difficult problem by using a system of three coupled no-linear differential equations. In his model there is a transition from a non-magnetic state to one with periodically reversing fields as W increases, followed by a periodic modulation of the basic cycle and then by chaos.

Solanki (Switzerland) reported new results on the dynamics of flux tubes and emphasized the observed oscillations, his report followed by new exciting results from Roberts(UK) and Ulmschneider(Germany) on the theoretical interpretation of the wave activity on flux tubes. Special emphasis was given on the generation of these oscillations.

A highlight of our conference was the new and exciting results from Ulysses experiment. Sanderson(UK) and Sarris(Greece) reported a variety of new and still unexplained features of the energetic ions and their association with activities in the solar surface.

The coupling of the Heliosphere with the solar corona was studied in depth in this conference and a number of reports presented new results on the flows (Schmieder(France)), chromospheric dynamics (Carlsson(Norway)), forced reconnection in restructuring magnetic field (Nordlund(Denmark)) and energy release processes (Benz(Switzerland)). Finally this unified picture was further extended to include the latest results n the energetic particles associated with solar explosion (flares). Trottet(France) presented for the first time a unified picture of the processes responsible for energy release in flares and the acceleration of energetic particles.

The highlight of the meeting was the special session on the recent results on SOHO. New and exciting areas of research, especially for young scientists, are opened up. Europe plays a key role in this mission and several new discoveries on coronal heating and coronal streamers were presented during the conference.

Planning on the new instrumentation and organizing the data for future use was an important contribution to Solar Physics research in Europe.

Participants: The meeting attracted more than 150 participants, 60 participants were under 30 years old.

Finances: EEC funds cover the expenses of the young participants and partially the expenses of 5 invited speaker. National funds cover most of the running costs of the meeting.
 

The Summer School:

• Attracted young and talented candidates from many European Universities.
• Offered a solid set of lectures in physics, with emphasis on new and original issues raised by solar physics (most lecturers are at the front edge of modern physics)
• Combined theory and practice through the use of the SOHO data
• Exposed students to the multiple aspects of a Space (solar) Mission (SOHO)
• Provided strong knowledge in data analysis
• Broadened the views of those who already work in Solar Physics and work on the analysis of SOHO data.

The Program of The School

The Summer School took place in Orsay from September 1 to September 13. The program was divided into twenty-five lectures (overall thirty seven hours) and practical works (twenty-six hours). Moreover four sessions of "free discussion" were scheduled in order to promote exchanges between lecturers and students. A visit of the Calibration Facility was also organized. Lectures were concluded by a presentation of ESA scientific projects by R.M. Bonnet, ESA Director of Scientific Programs. Each lecture was ninety minutes long and practical works could extend until 18.00 and beyond. A presentation of the results of the thirteen groups working on the thirteen topics was made during the last morning session of Saturday 13. Each presentation was followed by a general discussion.

The details of the lectures along with the contents of the practical works can be found in the booklet which was distributed to all participants.

Participants:More than eighty five people applied for the School, of whom thirty five were selected. They came from most European countries. They had a unique opportunity to meet fifteen internationally recognized experts in the field, coming from nine European countries. Some lecturers stayed a full week to supervise some practical works, to attend other lectures and to discuss with students. The I.A.S. provided half a dozen assistant teachers for practical works; most of them, being young, also served as students/organizers "go-between".

Finances: More than 17 students and 12 teachers were supported from EEC. National funds were used to cover the running expenses of the school.
 

Solar Physics at the end of the millennium is a field of research in rapid development. The Sun is the only object in the universe in which all four forces of nature have now been observed at work directly. The Sun is also sufficiently nearby that the matter which it ejects into space in the form of a high-velocity wind has been observed in situ. Finally, it is the source of life on Earth which it controls by its light. More subtle effects (Solar-Terrestrial Physics and Space Weather) on the terrestrial magnetic environment are also linked to solar activity through the solar particles, the solar wind and its perturbations such as coronal mass ejection. It, therefore, comes as no surprise that Solar Physics has a large outreach towards other branches of science, and towards mankind in general.

The 9th European Meeting on Solar Physics in Florence was organized by the Solar Physics Section of the Joint Astrophysics Division of the EAS and EPS. The theme chosen was a physical principle, the solar magnetic field. The work discussed at this Euroconference addressed the Sun outside its immediate core but well within the heliosphere. The programme was grouped around eight key problems on which recent progress has been striking. To ensure the educational and training goal of the conference, most reviewers went at large efforts to outline the physics, the recent progress, and the unsolved problems. Also, the SOC (G.M. Simnett, chair; C. Chiuderi, co-chair) and the LOC (G. Poletto, chair; E. Landi Degl' Innocenti, co-chair) have made every effort to invite young review speakers and support young applicants. The key problems addressed by the conference are itemized below:

Helioseismology. The hope that the SOHO satellite would allow the study of gravity-modes, and reveal the inner core of the Sun has, unfortunately, not materialized. However, detailed observations of the pressure modes have allowed the determination of the internal rotation rate of the Sun to a high accuracy. At the base of the convection zone where, traditionally, the solar magnetic field is believed to be stored, a sharp peak in the sound speed has been observed. From the observations of traveling pressure wave packets it has been possible, for the first time, to perform tomographic imaging of emerging magnetic fields.

Waves. A large variety of running and standing waves and oscillations have now been observed in the upper atmosphere and studied theoretically. The richness of the oscillatory modes in the solar atmosphere is primarily a result of the existence of strong inhomogeneities and non-uniformities created by spatially intermittent magnetic flux tubes anchored below the photosphere. Important progress was presented on the development of nonlinear and shock waves, and on nonlinear coupling of various waves in flux tubes.

Solar prominence. These objects are perhaps the most beautiful structures in the solar corona. Physically, they form a stepping stone in our understanding of the dynamics of the solar atmosphere, as they are magnetically dominated structures at coronal levels while their evolution is governed by (sub)photospheric fluid motions at their footpoints. Observations show that the prominence gas is made up out of ever-changing fibrils or threads, of which the diameter may go down to 200 km. A variety of wave modes has been observed, and can be used diagnostically.

Coronal heating. Explosive events appear to be a natural result of the reshuffling of the solar magnetic “carpet” arising from convective flows of magnetic flux tubes towards the network boundaries. Microscale heating has nowbeen observed down to 10²⁴ ergs per event. If the frequency distribution of such events continues with the same slope down to energies of 4x10²² ergs, the entire quiet corona could be heated by such explosions.

Solar flares. Impressive results were presented both on 3D numerical modeling of magnetic explosions, and on new analytical developments regarding quasi-separatrix layers which plays an important role in the flare phenomenon. There are many observations performed at X-ray wavelengths which suggest that magnetic reconnection plays an important role in the flare energy release.

Particle acceleration. This has been a long-standing problem in solar physics. Here, the key question is how a large fraction of the available energy in a solar flare is fed into particle acceleration. Sub-second timing studies and time-of-flight delay measurements in radio and hard X-ray emission show that particle acceleration in a flare is probably the result of acceleration by low-frequency MHD waves.

Coronal Mass Ejections and Space Weather. This has developed into a mature subject since the advent of SOHO. Dynamic 3D MHD modeling of Coronal MassEjections allows for the reproduction of white light structures and dimmings in X-rays. It is now understood that pressure variations in the solar wind excite oscillations of the Earth's magnetosphere while changes in the Interplanetary Magnetic Field cause reconnections in the terrestrial field and non-recurrent magnetic storms.

Solar wind and the heliosphere. The solar wind consists of slow/dense and fast/dilute streams, originating respectively in closed magnetic structures and in coronal holes. It now appears that the fast solar wind is simply the result of heating in open field regions, often in the form of explosive events. On the other hand, heating in closed magnetic structures, at a relatively large gas pressure, can lead to a slow and dense wind. Satellite observations with Ulysses have demonstrated the existence of large amplitude magnetic field fluctuations near the poles, creating field reversals in the wind.

Participants: The meeting attended more than 240 participants, a large fraction of them were young scientists.

Finances:EEC funds covered the expenses of 29 young participants and partially two invited speakers.

Summary:

It has to be stressed that, in recent years, the European solar community has diversified considerably because of the great number of physical and astronomical methods involved, while, at the same time, a coherent picture of solar physics from deep inside the Sun to large distances is gradually emerging. It is, therefore, of utmost importance that a conscious effort is made to strengthen the coherence of the community and its interdisciplinary links. In this respect, the Solar Physics Section of the EPS and of the EAS can play an essential role, and it is a pleasure to see that two important solar European organizations, JOSO and CESRA, have brought their expertise into SPS, without losing any of their impetus. It is gratifying to see the high quality of the work presented at the conference in terms of innovative ideas, numerical and analytical breakthroughs, and originality of instrumental designs, despite the relative modest level of funding when compared to the US. To put it simply, the scientific return per euro spent in European solar physics is high!

Publications:
 

Title	Editors	Publisher
Solar and heliospheric plasma physics	G.M. Simnett, C. Allisandrakis, L. Vlahos	Lecture Notes in Physics, Springer Verlag, 1997
Space solar physics	J.C. Vial, K. Bocchialini, P. Boumier	Lecture Notes in Physics, Springer Verlag, 1998
Magnetic fields and solar processes, Vols. I and II	A. Wilson	ESA. 1999

 
 
 

Progamme of events:
 

Event 1	Event 2	Event 3
Solar and Heliospheric plasma physics Dates: 13-18 May 1996     Place: Halkidiki, Greece,	Space solar physics   Dates: 1-13 September, 1998   Place: Orsay, France	Magnetic solar processes   Date: 12-18, September 1999   Place: Firenze, Italy